Method of introducing prestress to beam-column joint in triaxial compression

Abstract

There is provided a method of prestressing a beam-column joint with an appropriate ratio among the magnitudes of compression in the directions of X, Y, and Z axes. The method introduces prestress in a beam-column joint with a tensile introducing force generated by tensionally anchoring prestressing tendons that are arranged in PC beams extending along two horizontal directions (or X axis and Y axis) and PC columns extending along the vertical direction (or Z axis) and passed through the beam-column joint to bring the beam-column joint in triaxial compression, the prestress being introduced such that a diagonal tensile force T generated by an input shear force due to a seismic load of an extremely great earthquake that may occur very rarely will be cancelled completely or partially so as not to allow diagonal cracks to occur. The ratio of the prestresses introduced in the directions of the respective axes satisfies the following equation (1):σx:σy:σz=1:1:0.3−0.9   (1)where σx, σy, and σz are prestresses introduced in the directions of the X axis, the Y axis, and the Z axis respectively.

What is claimed is: 
     
       1. A method of introducing prestress in a beam-column joint that introduces prestress in a beam-column joint in a multi-story building structure constructed by prestressed concrete (PC) columns and prestressed concrete (PC) beams with a tensile introducing force generated by tensionally anchoring prestressing tendons that are arranged in the PC beams extending along two horizontal directions (or X axis and Y axis) and the PC columns extending along a vertical direction (or Z axis) and passed through the beam-column joint to bring the beam-column joint in triaxial compression, the prestress being introduced such that a diagonal tensile force generated by an input shear force due to a seismic load of an extremely great earthquake that may occur very rarely will be cancelled completely or partially so as not to allow diagonal cracks to occur, wherein the ratio of the prestresses introduced in the directions of the respective axes satisfies the following equation (1):
   σ x:σy:σz= 1:1:0.3-0.9   (1)
 
 
       where σx, σy, and σz are prestresses introduced in the directions of the X axis, the Y axis, and the Z axis respectively, which are calculated by the following equations:
     σx=Px/Ax, σy=Py/Ay, σz=Pz/Az,    
 
       where Px is the tensile introducing force in the direction of the X axis, Ax is a cross sectional area of the beam at an end with respect to the X axis, Py is the tensile introducing force in the Y axis, Ay is a cross sectional area of the beam at an end with respect to the Y axis, Pz is the tensile introducing force in the Z axis, and Az is a cross sectional area of the column at an end with respect to the Z axis. 
     
     
       2. A method of introducing prestress in a beam-column joint according to  claim 1 , wherein values of σx, σy and σz fall within the following ranges:
 2.0≤σx≤10.0 (N/mm 2 ) 
 2.0≤σy≤10.0 (N/mm 2 ) 
 0.6≤σz≤9.0 (N/mm 2 ). 
 
     
     
       3. A method of introducing prestress in a beam-column joint according to  claim 2 , wherein at least five layers of the building structure are grouped, and the prestress σz introduced in PC columns in the layers of a same group is uniformized. 
     
     
       4. A method of introducing prestress in a beam-column joint according to  claim 3 , wherein the prestress is introduced such that when a diagonal tensile force generated in the beam-column joint by the extremely great earthquake is partly cancelled and partly remains, a tensile stress intensity resulting from the remaining diagonal tensile force will be equal to or lower than an allowable tensile stress of the prestressed concrete in the beam-column joint. 
     
     
       5. A method of introducing prestress in a beam-column joint according to  claim 2 , wherein the prestress is introduced such that when a diagonal tensile force generated in the beam-column joint by the extremely great earthquake is partly cancelled and partly remains, a tensile stress intensity resulting from the remaining diagonal tensile force will be equal to or lower than an allowable tensile stress of the prestressed concrete in the beam-column joint. 
     
     
       6. A method of introducing prestress in a beam-column joint according to  claim 1 , wherein the prestress is introduced such that when a diagonal tensile force generated in the beam-column joint by the extremely great earthquake is partly cancelled and partly remains, a tensile stress intensity resulting from the remaining diagonal tensile force will be equal to or lower than an allowable tensile stress of the prestressed concrete in the beam-column joint.